Effects of Cold Water Temperatures on Water Treatment Unit Processes

摘要

This paper discusses results from a 16-month water treatment pilot testing program in Winnipeg, Canada (pop. 650,000) which evaluated a DAF/ozone/deep bed filtration process. Seasonal raw water temperature ranged from 0.3 to 23 °C. Pilot testing determined that the coagulation, flocculation and DAF design parameters were dictated by the cold water period. Cold water poses special challenges to coagulation, flocculation and DAF treatment. For the DAF process, bubble carry-over was a problem at higher loading rates since the higher water viscosity at low temperatures resulted in a lower bubble rise rate. It was found during cold water periods that DAF loading rates had to be reduced and recycle air loading rates had to be increased. Additionally, because coagulation reactions are slower at low temperatures, higher coagulant doses and additional flocculation time was required to form a floatable and filterable floc. It was also found that cold water temperature affected the performance of various coagulants and coagulant aids tested and adversely affected filter ripening times.